Leaf area – sapwood area relationships in adjacent young Douglas-fir stands with different early growth rates

Abstract

The relationship between foliage area and sapwood basal area was studied in three adjacent 22-year-old Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco) stands that differed in early growth rates. Sapwood width was fairly constant for most of the stem above the stump, but the number of annual rings in the sapwood decreased gradually with height. Sapwood area also decreased with increasing height in the tree, the stands differing significantly only at breast height. The proportion of heartwood from stump to near the base of the crown was significantly higher for the stand of fastest early growth. Ratios of leaf area to sapwood area were significantly higher for that stand and varied in every stem section, the ratio lower at breast height than at the base of the live crown. At the base of the crown, the ratio of leaf area to sapwood area was 1.33 and 1.57 times greater in the fast-growing stand than in the intermediate- and slow-growing stands, respectively. Leaf area was as closely related to dbh as to sapwood area at breast height. Sapwood area at the crown base was more accurate than sapwood area at breast height for predicting leaf area in the fast stand and was equally accurate in the other two stands. Ratios of leaf area to sapwood area correlated positively with sapwood ring width. However, because sapwood ring width also correlated closely with sapwood area, it did not improve predictive equations. The results suggest that the "pipe model" theory must be modified to account for the internal structure of the "pipe" and that caution should be exercised when using published leaf area to sapwood area ratios.